The reason your edit occasionally fails is because, somewhere, you're opening up another browser window while you're previewing a topic, and then you click the "back" button. What this does (and I can only vouch for IE) is that it either flushes the edit textbox or goes back to a cached version. What this results in is an (apparent) total loss of your changes. If you're lucky enough to catch this problem, simply click the "forward" button and save your changes. If you're UNlucky (like I was the first time I saw this), you will lose a LOT of changes! I don't know how to fix this, because it's a browser problem, not a TWiki problem.

I do agree, though, that having a "Save and continue editing" button would be nice

The caching problems experienced with browsers are discussed in Support.BrowserIssues - please contribute there, as I'd like to get this sort of browser/cache behaviour documented. It does seem that IE5 usually manages to cache the previously entered TEXTAREA state, but not always!

When I would have to choose between "Cancel edit" and "Back", I would choose Cancel. Back is already available with the browser's back button, while for "Cancel" there would be no alternative than to go back and click Cancel (or abandon the edit, leaving the edit lock closed). See DoNoGoBackTwiceToCancel.

But I found this principle useful for the changeform template. Somehow this page looks like a dead end.
In PatternSkin, I have implemented the above script as: